Info about St. Ives Input Transformer Vt26281 applications

[user 134807]

I've had two of these Input Transformers in a drawer for a while which were originally from an OB truck's rack. I think the passive 1u rack unit they came from was used to feed some amplifiers, and they had a small PCB with a switch to merge the two line inputs if required. Not knowing much about them at the time I contacted Carnhill (who have some connection with St.Ives) and was told that they were recently remade as VTB 9071, but were originally a custom design for Neve equipment.
I'd like to know what these would be best suited for, given that they have a 2+2:1+1 designation- which I don't really understand I take it they aren't balanced, and I have tinkered with the primary and secondaries such that I managed to get some gain from them. Whether this is a substitute /compliment for opamp gain or not is something I'd like to understand a bit more fully. What would you use them for?

 

[TwentyTrees]

Nice find! Bit confused by the datasheet though. I'm not an expert in magnetics - but if either side can be wired 10k or 2.5k, doesn't that make it a 1+1:1+1 with a possible step up or down of 6dB? (√10k:√2500 = 100:50 = 2:1)

They'd work well as standard 1:1 or 2:1 input transformers - as the latter, might be spot on for a TG-style compressor for example.

 

[user 134807]

Nice find! Bit confused by the datasheet though. I'm not an expert in magnetics - but if either side can be wired 10k or 2.5k, doesn't that make it a 1+1:1+1 with a possible step up or down of 6dB? (√10k:√2500 = 100:50 = 2:1)

They'd work well as standard 1:1 or 2:1 input transformers - as the latter, might be spot on for a TG-style compressor for example.

Thanks! I did find the data sheet puzzling too. I think I managed around a 6db gain now you mention it although maybe it's determined by what you feed it with. The guy from Carnill didn't know its original application and It made me more interested in what it specifically did that required the double designation in the turns ratio. I'll have to look up the TG stuff to know more about it, but I suppose it would be a shame not to put it to full use if it had other specific useful applications. Short of that I will probably try to use it in a more standard way

 

[sahib]

.............
I'd like to know what these would be best suited for, given that they have a 2+2:1+1 designation- which I don't really understand I take it they aren't balanced, and I have tinkered with the primary and secondaries such that I managed to get some gain from them.............

You have sort of answered your own question.

2+2 :1+1 indicates that the transformer has four windings. Two separate windings on one side (2+2) and two separate windings on the other side (1+1). The turns ratio between these two sides is 1 to 2, or 2 to 1 depending on which side you apply the signal to and which side you take it from. So, it either steps up or steps down the signal level (guess how you must have wired it).

It is a line input transformer.

Twenty Trees is not alone in confusion. Stated impedance ratio does not make sense. This was discussed in another thread. Sowter also has this ambiguity. My assumption is/was that the transformer was designed to work into specific impedances but that still does not reconcile with the maths in terms of turns ratio.

 

[user 134807]

These things are still a bit mysterious to me lol. It does make more sense now, Thanks Sahib.

 

[CJ]

I bet it is a typo.

Neve inputs are dual coil affairs usually wound pri/sec.

They use a small core so there is no room for interleaving.

DCR would indicate a 1:1 ratio , the sec DCR being larger because the sec is wound last.

 

[ruffrecords]

This looks like it is Carnhill's version of the Neve 31267 transformer made by St. Ives and others. It is a line input transformer and was normally strapped as 10K:600. To the best of my knowledge, Neve never had a 1:1 transformer, they were all step up or down. The datasheet is definitely wrong.

Cheers

Ian

 

[user 134807]

Thanks CJ and ruffrecords. This info led me into interesting territory, namely-
https://groupdiy.com/threads/neve-31267-setup-question.33778/and
https://groupdiy.com/threads/damping-transformer-ringing-zobel-network-question.32441/This should keep me busy for a while. Cheers!

 

[Tekay]

Marinair made a line bridging transformer, T1448 10k/2,5k : 9,6k/2,4k(serial/parallel)

 

[CJ]

interesting, i bet it is a 1:1 with dcr losses factored into the sec z specs,
10K:10K more turns of thinner wire so dcr will be higher than a 600:600.

typical 600 dcr will be around 15-20 ohms, 10K above says 220,